Radar systems used to detect the presence, position, and other characteristics of both natural and man-made objects are critical to both civilian and military operations. These systems typically transmit “beams” or electromagnetic (EM) signals toward targets, and process reflected return signals (or echoes) for object identification and characterization. The presence of clutter in these return signals creates a significant technical challenge in accurately processing return signals. This clutter decreases radar performance by hindering the system's ability to detect targets and/or increases the probability of a false target detection.
The negative effects of this received clutter can be reduced by the radar system's ability to produce multiple coherent pulses. This radar “stability” includes the radar transmitter's ability to generate uniform pulses that have consistent amplitude and phase from pulse to pulse. In particular, in current moving target indicator (MTI) radar systems, for example, pulses received from the target are delayed in time until the arrival of a second pulse. The first delayed pulse is then subtracted from the second pulse. As a result, stationary clutter is cancelled, and a moving target is more readily identifiable. However, the effectiveness of these clutter reduction methods is limited by the degree to which the transmitted pulses within a coherent interval do not perfectly replicate one another (i.e. instability). For example, when a transmitter power supply voltage changes from pulse to pulse (transmitter “push”), phase and amplitude modulations are produced in the signal, thus degrading clutter cancellation. This is particularly the case when the pulse repetition frequency (PRF) changes from coherent interval to coherent interval. This instability is often difficult to detect and isolate. As a result, clutter rejection requirements of modern radar systems can impose very strict pulse-to-pulse stability requirements on the radar system's electronics, which can considerably increase system cost.
Attempts have been made to address these problems by extracting or compensating the pushing factor from large clutter returns. More specifically, amplitude and phase data from these returns obtained from clutter processing are used to create compensation factors which adjust weights applied during Doppler processing. Such techniques have several drawbacks. For example, they utilize average pushing errors, and thus averaged cancellation factors to reduce clutter based errors, target contamination errors, and antenna motion errors, despite the fact that these errors actually vary pulse-to-pulse.
Accordingly, alternative methods and systems for increasing transmitter stability in a radar system are desired.